1. Field of the Invention
The present invention relates to a contract management device for use in the charged broadcast service in which broadcast delivered contents are to be decrypted according to contract terms (period, viewable or listenable channels), and a broadcast reception device in which contents decryption is controlled by the contract management device.
2. Description of the Background Art
There are increasing demands for the enhancement of services by the digital broadcasting as the digitalization progresses from the communication satellite (CS) to the cable TV and the terrestrial broadcasting, and it is expected that the digital broadcasting will play the leading role in the future broadcast services.
The most significant feature of the digital broadcasting is that, due to the introduction of the data compression technique, the utilization efficiency of frequencies required in broadcasting programs can be improved and the number of broadcast channels can be increased considerably compared with the analog broadcasting. In addition, as it is possible to apply the highly sophisticated error correction technique, it is possible to provide uniform services in high quality.
By the digitalization of the broadcasting, it becomes possible to provide multimedia services using a variety of information forms (video, audio, text, data, etc.), and many systems for providing such services have been appearing recently.
In such a system, in the case of providing a charged broadcast service in which scrambled contents are to be descrambled or encrypted contents are to be decrypted according to the contract period, there is a need to be able to carry out the customer management in accordance with contract periods. Here, the customer management in accordance with contract periods implies an ability to make programs of contracted channels viewable or listenable only within the contract period for which the required fee has been paid, for example.
In addition, there is a need to provide the key information, which is necessary in decrypting encrypted contents or descrambling scrambled contents at the reception device, only to the proper viewers or listeners (according to the contracted channels and the contract period) and without failure, from a viewpoint of preventing the improper viewing or listening.
In this regard, conventionally, a unique master key is provided for each broadcast reception device separately, and only work keys of the contracted channels are sent to each viewer or listener with a reception contract by encrypting them using the corresponding master key. Here, the work key is a key uniquely defined for each channel, which can decrypt a channel key of that channel that is broadcasted in an encrypted form. The channel key is used in descrambling scrambled broadcast contents.
In addition, this work key is to be set up for each contract period (usually one month), and sent from the broadcast station whenever the contract is renewed, so that there is a need to sent necessary and sufficient amount of work keys to respective contractors at each contract period. This scheme has an advantage in that the contract period can be faithfully obeyed by updating the work key. However, as long as this scheme is adopted, it is necessary to broadcast the work keys to all the contractors every month, which is becoming a severe requirement in view of the required amount of transmission because of the increasing number of contractors and channels for the CS broadcasting. In particular, this requirement is very hard to satisfy in the broadcasting service with respect to mobile reception devices which is expected to be associated with a poor reception state, a short reception time and a narrow bandwidth.
It is therefore an object of the present invention to provide a conditional access broadcast system using a broadcast reception device and a contract management device which is capable of realizing conditional access while maintaining the safety level even when the broadcast bandwidth available to transmission of information related to the conditional access is narrow or when the number of contractors increased beyond the expectation.
According to one aspect of the present invention there is provided a broadcast reception device, comprising: a memory for storing a master key commonly provided with respect to a plurality of broadcast reception devices and one reception device ID uniquely assigned to said broadcast reception device; a reception unit for receiving encrypted contents information delivered from a broadcast station by broadcast; a decryption unit for decrypting encrypted reception contract information using the master key and the encrypted contents information using a channel key, the encrypted reception contract information being received from the broadcast station and containing at least a contract information for controlling decryption of the encrypted contents information and a reception device ID in correspondence; and a control unit for selectively acquiring one contract information corresponding to a reception device ID that coincides with said one reception device ID, from the encrypted reception contract information decrypted by the decryption unit, and controlling whether or not to give the channel key to the decryption unit according to said one contract information.
According to another aspect of the present invention there is provided a contract management device, comprising: a management unit for managing contract information for controlling decryption of encrypted contents information delivered from a broadcast station by broadcast, with respect to a plurality of broadcast reception devices each of which decrypts the encrypted contents information according to the contract information; and a delivery unit for delivering to said plurality of broadcast reception devices a reception contract information containing at least the contract information and a reception device ID in correspondence, the reception device ID being uniquely assigned to each broadcast reception device, by encrypting the reception contract information using a master key which is commonly provided with respect to said plurality of broadcast reception devices.